1. Field of the Invention
The present invention generally relates to integrated circuit computer aided design (CAD) software tools. Specifically, the invention describes a method, which is implemented in software, of modifying or masking output events of bi-directional signals in event-format test pattern files used in digital logic integrated circuit CAD environments.
2. Description of the Related Art
When digital microchips are tested, known signals are input to the chip, and the resulting output is compared with expected signals. If the output signals match the expected signals, then the chip is determined to be good. If not, then the chip is determined to be defective. The combination of input and output signal patterns are called test patterns.
Event-format test pattern files are known as a type of file for recording signal patterns for the testing of digital logic integrated circuits. In event-format files, signal patterns are described by statements which indicate the event time of signal transitions and the logic value which the signal transitions to. Event formats do not include statements which indicate a signal""s logic value when no transitions occur.
Often, portions of the output signals are irrelevant to the test. That is, it doesn""t matter what state those output signal portions are in, as they do not affect whether the chip is good or defective. These irrelevant portions of output signals then should be xe2x80x9cmaskedxe2x80x9d, or excluded from the test, so that they are not compared with expected values, because if they were not masked, the microchip could be determined to be defective when it is not.
The pertinent aspects of event file formats of concern in this invention are as follows. There must exist a main event-format file or set of files which include data for input signals, output signals, and internal directional control signals for bi-directional pins. There must exist a secondary event-format file or set of files which include the modified output values or masking information for output periods of bi-directional signals. There may exist other peripheral files which are used to determine correspondence of signals in the event files with actual pins on the chip if this information is not included in the files mentioned previously. There may also exist files which determine correspondence of the internal bi-directional control signal with the external bi-directional pins if this information is not included in the files mentioned previously.
It is sometimes required to modify or mask the output events of bi-directional signals in the main event-format file or files. Presently, modifications of output events in these event-format files are done by manually modifying the events in a file using a text editor. Since in many modern designs, most pins are bi-directional, and patterns can be up to hundreds of thousands of cycles long, this method is both time consuming and error prone.
Accordingly, an object of the present invention is to efficiently automate the modification and masking of output events of event-format files in order to reduce the manual work load, reduce the overall time to accomplish the task, and to reduce the chance of human error.
Another and more specific object of the present invention is to provide a computer-readable recording medium storing a method of masking or modifying output events of bi-directional signals in an event-format test pattern file, whereby the aforementioned objectives are achieved.